JPS6329633B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an aluminum-clad steel sheet using steel as a core material and aluminum or an aluminum alloy as a skin material. In the conventional manufacturing method of aluminum-clad steel sheets by pressure welding, the steel plate and aluminum plate are stacked and pressed together in a rolling mill, and then diffusion softening annealing is usually performed for the purpose of interdiffusion and recrystallization softening of the welded layer. It was hot. However, in this case, since the product plate thickness is obtained in the pressure welding process, it is impossible to manufacture uniform products with good plate thickness dimensional accuracy on a large-scale industrial production line. In an attempt to improve this, if a finish rolling process is adopted after diffusion softening annealing,
This time, the product will remain as rolled, making it impossible to produce aluminum-clad steel sheets that are soft and have good workability. Furthermore, even if softening annealing is performed after this, if the finish rolling rate is small, recrystallization softening of the core material (steel plate) is difficult to occur.
Problems arise in terms of mechanical properties. For this reason, it has been proposed to insert a finish rolling process between the pressure welding process and the diffusion softening annealing process. In this case, the accuracy of the product plate thickness can be better controlled, but the problem of peeling of the pressure layer occurs during the finish rolling process. This peeling during finish rolling can be practically avoided by increasing the rolling reduction rate in the welding process to about 60% or more, but this requires a powerful and large rolling mill, which is an equipment problem. arise. The purpose of the present invention is to solve various problems in the conventional manufacturing method of aluminum-clad steel sheets using pressure welding, and in particular, to provide a method for manufacturing aluminum-clad steel sheets with excellent design with good manufacturability. It is. For these purposes, the present invention includes a pressure welding process in which a laminated plate in which aluminum or aluminum alloy plates are laminated on at least one side of a mild steel plate is pressed by rolling, and the obtained press-welded plate is subjected to recrystallization softening of the steel plate layer. A diffusion annealing process in which the aluminum or aluminum alloy plate is annealed under conditions that substantially do not cause recrystallization and softening of the aluminum or aluminum alloy plate to promote interdiffusion of the pressure bonding layer, and the resulting clad plate is rolled at a rolling ratio of 20% or less. An aluminum clad steel sheet is manufactured through a finish rolling process in which aluminum or aluminum alloy is rolled at the base, and then a softening annealing process in which the clad plate is annealed under conditions in which the aluminum or aluminum alloy becomes coarse grains. According to the method of the present invention,
Aluminum-clad steel sheets with excellent design can be manufactured with good manufacturability (in other words, without using a large rolling mill, on a mass production line with good controllability of dimensional accuracy). The pressure welding process in the present invention can be carried out under a slight pressure reduction ratio of 30 to 60%. Even if finish rolling is performed later (that is, after diffusion annealing), the problem of peeling does not occur during finish rolling under this light pressure reduction ratio. The next diffusion annealing step differs from conventional diffusion softening annealing in that it is performed under conditions that do not cause recrystallization softening of the steel sheet layer. The annealing temperature in this diffusion annealing is 300~
It is recommended that the temperature be within the range of 450℃. Mutual diffusion of the core material (steel) and skin material (aluminum) in the pressure welding layer progresses,
In addition, a temperature of 300°C or higher is required for recrystallization of the skin material. In addition, the recrystallization softening of the core material does not occur,
In addition, in order to prevent the skin materials from adhering to each other due to the winding force of the coil, the temperature needs to be 450°C or less. This annealing method can be batch annealing using a tight coil, but in this case the annealing time is preferably about 5 to 20 hours. The diffusion annealing process of the present invention can be carried out using other annealing methods, but whichever annealing method is adopted, interdiffusion of the pressure bonding layers can proceed without causing recrystallization softening of the core material, and the skin material It is necessary to select conditions that will realize recrystallization softening. One of the characteristics of the method of the present invention is that finish rolling is performed after diffusion annealing under such conditions, but when performing this finish rolling, the reduction rate is 20% or less, preferably 10%. This finish rolling is carried out under the following conditions. As shown in the examples below, there is a close relationship between the rolling reduction in this finish rolling process and the surface grain size of the skin material, and when this rolling reduction is 20% or less, the surface grains have a design quality. It was found that the grains became coarser (Table 1). This finish rolling adjusts the final thickness of the clad steel plate, but in this finish rolling process, although it is annealed first, the core material retains the rolled structure from pressure rolling. This is different from conventional finish rolling. However, since the skin material has been completely recrystallized and softened by the previous diffusion annealing, the reduction rate adjustment in this finish rolling (actually,
The crystal grains of the skin material can be conveniently adjusted by adjusting the grain size to 20% or less, and thereby the improvement in design, which is one of the objectives of the present invention, can be achieved. The final softening annealing step is carried out under conditions that make the crystal grains of the skin coarse, but the conditions also need to be such that the development of the Fe--Al alloy layer is suppressed. Therefore, the annealing temperature in this softening annealing is preferably 500 to 570°C. When batch annealing is performed, the annealing time is preferably about 2 to 24 hours. In order to coarsen the crystal grains of the skin material, a temperature of at least 500°C is required, but if the temperature exceeds 570°C, the Fe-Al alloy layer tends to develop. When this alloy layer develops, the alloy layer is exposed on the surface, resulting in a significant impediment to the design. According to the method of the present invention, since the core material is recrystallized for the first time in this final annealing, the crystal grains of the core material can be adjusted in this final step, and the core material has crystal grains that are preferable from the viewpoint of workability. It can easily be used as a core material. In this way, by adopting the four processes of pressure welding process, diffusion annealing process, finish rolling process, and softening annealing process, and specifying the conditions described above for each process, we can eliminate the conventional method that lacks any of these conditions. Aluminum-clad steel sheets with superior design and high bonding strength can be manufactured with good productivity. Example 1 A rimmed cold-rolled steel sheet with a thickness of 1.8 mm was immersed in a solution of 5 wt.% sodium orthosilicate at 85°C for 2 minutes to degrease it.
The material that had been washed and dried was used as a core material. Also,
A 1.0 mm thick aluminum plate of JIS 1100H24 was used as the skin material after being solvent-degreased by spray cleaning with trichloroethane. A skin material was superimposed on one side of this core material, and the material was pressed and rolled in a four-high rolling mill. The pressure welding speed was 19 m/min on the exit side. The work rolls of the rolling mill were heated to approximately 90°C before pressure welding. The pressure reduction rate was 52% of the total thickness of the core material and skin material, and the total thickness after pressure welding was 1.34 mm. The pressure reduction rate was 48% for the core material only, and 60% for the skin material only. The obtained press-welded plate was charged into a batch annealing furnace,
Diffusion annealing was performed at 350°C for 15 hours in the coiled state. Next, finish rolling was carried out while varying the rolling ratio from 2 to 30%. Then, the obtained clad plates were coated with an anti-adhesion agent, placed in a batch annealing furnace, and subjected to softening annealing at 550°C for 5 hours. The obtained aluminum-clad steel plate was etched for 1 minute with an aqueous solution of hydrofluoric acid (1 volume of hydrofluoric acid (40 wt%) to 4 volumes of distilled water). Table 1 shows the relationship between the finishing rolling rate and the average grain size of the skin material. The appearance after etching at a typical finish rolling rate is shown in the photographs in Figures 1 to 3. Figure 1 shows the finish rolling rate of 2%, Figure 2 shows the finish rolling rate of 5%, and Figure 3 shows the finish rolling rate of 10%.
, and the magnification of each is 10x. From these results, it can be seen that if the finish rolling rate is 20% or less, the grain size becomes large and the steel sheet can be used as an aluminum clad steel sheet with good design. 【table】

[Brief explanation of the drawing]

Figures 1 to 3 are metallurgical micrographs (x10x) showing the surface conditions of clad steel sheets obtained by the method of the present invention. Figure 1 is for a finish rolling ratio of 2%, and Figure 2 is for The one with a finishing rolling rate of 5%, and the one in Figure 3 with a finishing rolling rate of 10%.

Claims (1)

[Claims] 1. A pressure welding process in which a laminated plate in which aluminum or aluminum alloy plates are laminated on at least one side of a mild steel plate is pressed by rolling, and the obtained press-welded plate is subjected to recrystallization softening of the steel plate layer. a diffusion annealing step in which interdiffusion of the pressure bonding layer is promoted by annealing under conditions that substantially do not cause recrystallization softening of the aluminum or aluminum alloy plate;
It consists of a finish rolling process in which the obtained clad plate is rolled at a rolling rate of 20% or less, and then a softening annealing process in which the clad plate is annealed under conditions where aluminum or aluminum alloy becomes coarse crystal grains. A manufacturing method for aluminum-clad steel sheets with excellent design. 2. The method for manufacturing an aluminum clad steel sheet according to claim 1, wherein the diffusion annealing step is carried out at a temperature range of 300 to 450°C. 3. The method for manufacturing an aluminum clad steel sheet according to claim 1 or 2, wherein the softening annealing step is carried out at a temperature range of 500 to 570°C.